1. Field of the Invention
Aspects of the present invention relate to an optical transmission control circuit used with an optical communication module (OTR) and in particular to an optical transmission control circuit for storing digital diagnostic monitoring (DDM) information to provide stable optical communication performance and outputting necessary DDM information to a host apparatus.
2. Description of the Related Art
An optical transmission control circuit in a related art inputs a plurality of analog signals relating to DDM information of the optical transmission control circuit and becoming operating parameters, converts the analog signals into digital values, stores the digital values in a digital value storage section, makes a comparison between the digital value and a threshold value, and stores a flag value in a flag value storage section based on the comparison result. Accordingly, the host apparatus reads the flag value from the flag value storage section in the optical transmission control circuit through an interface circuit on a regular basis or according to an error notification as an interrupt from the optical transmission control circuit. The host apparatus further reads the digital value in response to the read result of the flag value. Accordingly, to investigate an anomaly occurring in the optical transmission control circuit, it is made possible for the host apparatus to first read the flag value and then read the digital value only about the important part; the monitor operation can be simplified (see JP-B-3822861)